Spinal and Bulbar Muscular Atrophy (SBMA) is a progressive neuromuscular disease affecting the proximal spinal and bulbar motor neurons and the skeletal muscles. To date, there is no effective cure for this devastating disease. SBMA arises from the expansion of a polymorphic CAG trinucleotide repeat in the Androgen Receptor (AR) gene, resulting in an expansion of glutamines in the AR protein. Polyglutamine expansion renders the mutant AR protein toxic, resulting in the formation of mutant protein aggregates and cell death. The overarching goal of this project is to better understand the cellular and molecular mechanisms underlying the pathogenesis of SBMA with the hope that such insight will lead to the development of better therapeutics. In order to reach this goal, we began by identifying factors that could potentially modulate the SBMA disease condition in vivo. The preliminary data presented in this application clearly show that Nemo-Like Kinase (NLK), an evolutionarily conserved serine/threonine kinase, is a key factor that could potentially modulate the SBMA disease condition. In this proposal, we will test the idea that NLK can modulate SBMA pathogenesis via regulating the posttranslational modification or expression of the mutant AR. To investigate this idea, we propose the following three specific aims. In Aim 1, we will determine whether NLK can modulate SBMA-related phenotypes using mouse as a model system. We will utilize several SBMA mouse models that are characterized by both neuromuscular pathology and behavioral deficits. Specifically, (1) we will first test whether constitutive loss of one functional Nlk allele (50% NLK reduction) suppresses the neuromuscular phenotypes of SBMA. (2) We will also evaluate the role of NLK in SBMA in a tissue-specific manner by using Nlk conditional knockout mice. We will focus on motor neurons and skeletal muscle, as they are known SBMA- affected tissues. In Aim 2, we will identify the molecular mechanism by which NLK regulates the SBMA disease condition. We will determine how NLK kinase activity is responsible for mediating the neuromuscular phenotypes of SBMA. The role of NLK in (1) AR posttranslational modification and (2) AR protein degradation/clearance will be determined and their contribution to SBMA toxicity will be characterized. In Aim 3, we will determine the role of the peptidyl-prolyl isomerase Pin1 in SBMA pathology. We will test whether Pin1 acts downstream of the NLK-induced effects on mutant AR to modulate toxicity in SBMA. To do this, we will utilize cell culture approaches and Drosophila and mouse genetics. We believe that the knowledge gained from the studies proposed in this application will advance our basic understanding of the cellular and molecular mechanisms underlying SBMA and will suggest new therapeutic interventions aimed at reducing the burden of SBMA and other neuromuscular diseases.